JP5572181B2 - Spark plug and manufacturing method thereof - Google Patents

Description

  The present invention relates to a spark plug used for an internal combustion engine or the like and a method for manufacturing the same.

  The spark plug is assembled in a combustion apparatus such as an internal combustion engine (engine) and used for ignition of the air-fuel mixture or the like. In general, the spark plug includes an insulator having an axial hole extending along the axial direction, a center electrode inserted through the tip end of the axial hole, and a metal shell provided on the outer periphery of the insulator. Further, on the outer peripheral surface of the metal shell, there are formed a screw part for screwing into the mounting hole of the combustion device, and a hook-shaped seat part formed on the rear end side of the screw part and projecting radially outward. Has been.

  Furthermore, in order to ensure airtightness in the combustion chamber, a ring-shaped gasket is provided on the screw neck of the screw portion, and when the ignition plug is assembled to the combustion device, the gasket is brought into contact with the seating surface of the combustion device. Is known (see, for example, Patent Document 1). In addition, from the viewpoint of realizing further excellent hermeticity, the front end surface of the seat portion is tapered toward the front end side in the axial direction without providing a gasket, and the tapered surface is directly on the seat surface. A contact method has been proposed. In the configuration in which the tapered surface is brought into contact with the seating surface in this way, the taper surface is made smooth with very little unevenness, and a wide range of the tapered surface is brought into contact with the seating surface. , See Patent Document 2).

JP 2008-108478 A Japanese Patent No. 4092826

  However, in the configuration in which the tapered surface is smooth as described above, there is a possibility that the airtightness may be significantly reduced by only attaching a small wrinkle to the tapered surface during the manufacturing process or the transportation of the spark plug. is there. Therefore, it is necessary to manage the taper surface very carefully during the manufacturing process and during transportation, which is inferior in productivity and ease of handling.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide excellent productivity and easy handling in a spark plug of a type in which a tapered surface comes into contact with a seating surface when assembled to a combustion device. It aims at ensuring favorable airtightness, realizing the property.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The spark plug of this configuration includes a cylindrical insulator extending in the axial direction,
A cylindrical metal shell provided on the outer periphery of the insulator;
The metal shell is
A threaded portion for screwing into the mounting hole of the combustion device;
A tapered surface having an outer diameter that gradually decreases toward the distal end side, and a bowl-shaped seat portion that is positioned on the rear end side of the screw portion;
When the threaded portion is screwed into the mounting hole of the combustion device, the tapered surface is a spark plug that contacts the seat surface of the combustion device,
In the range from at least the outermost peripheral portion of the tapered surface to a portion having an outer diameter of 95% of the outer diameter at the outermost peripheral portion, the taper surface has a ring shape or a spiral shape having a length of one or more rounds, and the main body A protrusion extending along the circumferential direction of the metal fitting is formed,
In the cross section including the axis, the arithmetic average roughness of the surface of the tapered surface within the range is 1 μm or more and 5 μm or less.

  In general, in the state where the ignition plug is assembled to the combustion device in which the seat surface is not deformed, an acute angle (the seat angle) among the angles formed by the outer surface of the seat surface and the axis in the cross section including the axis line. The inclination angle of the surface is smaller than the acute angle (inclination angle of the taper surface) of the angles formed by the outline of the taper surface and the axis. Therefore, when the spark plug is assembled to the combustion device, the portion (outer periphery) located within the range from the outermost peripheral portion of the tapered surface to the portion having an outer diameter of 95% of the outer diameter at the outermost peripheral portion Side region) contacts the seating surface of the combustion device. That is, the outer peripheral side region is a particularly important part in terms of maintaining airtightness in the combustion chamber.

  According to the above configuration 1, in the cross section including the axis, the arithmetic average roughness of the surface in the outer peripheral region is set to 1 μm or more, and the presence of slight unevenness is allowed. Therefore, even if there is a minute wrinkle, there is no great difference in the state of the taper surface, and it is not necessary to manage the taper surface with particular care during the manufacturing process or transportation. As a result, excellent productivity and ease of handling can be realized.

  On the other hand, when the arithmetic average roughness of the surface in the outer peripheral side region is 1 μm or more, there is a concern that the adhesiveness of the tapered surface to the seating surface is impaired and the airtightness becomes insufficient. In this regard, according to the above-described configuration 1, the outer peripheral side region is formed with an annular or one or more spirals and a protrusion extending along the circumferential direction of the metal shell. Accordingly, when the spark plug is assembled to the combustion device, the spiral or annular protrusion of the tapered surface can be brought into contact with the seat surface with a relatively large pressure. Furthermore, since the protrusion which contacts with a comparatively large pressure makes cyclic | annular form or 1 or more spirals, it can seal more reliably between a seat surface and a taper surface over the perimeter. As a result, excellent airtightness can be ensured.

  In order to realize excellent airtightness more reliably, the arithmetic average roughness of the surface in the outer peripheral region is preferably 5 μm or less.

Configuration 2. The spark plug of this configuration is the above-described configuration 1, wherein the protrusion is formed over the entire tapered surface,
The arithmetic average roughness of the surface of the tapered surface is 1 μm or more and 5 μm or less.

  Note that “the entire area of the tapered surface” refers to the entire area of the tapered surface that can contact the seating surface. For example, the range from the outermost peripheral portion of the tapered surface to the portion having the same outer diameter as the screw diameter of the screw portion can be referred to as the entire area of the tapered surface.

  According to the configuration 2, the spiral or annular protrusion is formed over the entire tapered surface. Therefore, even if the seating surface is deformed by repeatedly assembling / removing the spark plug to / from the combustion device, the spiral or annular protrusion formed at any position is removed from the seating surface. Can be contacted. For example, in a state in which it becomes difficult to contact the protrusion formed on the outer peripheral side region with the seat surface due to the deformation of the seat surface, the protrusion formed on the inner peripheral side of the outer peripheral side region is on the seat surface. It will come into contact. That is, according to the above-described configuration 2, even when the spark plug is assembled a plurality of times and the seat surface is deformed, good airtightness can be maintained.

  Configuration 3. The spark plug of this configuration is characterized in that, in the above configuration 1 or 2, the thread diameter of the thread portion is M14 or less.

  In the spark plug in which the screw diameter of the screw portion is M14 or less as in the configuration 3, the area of the tapered surface is relatively small. Therefore, the contact area of the taper surface with respect to the seating surface becomes small, and there is a concern about a decrease in airtightness. However, by adopting the above configuration 1 or the like, excellent airtightness can be realized even in a spark plug having a screw diameter of M14 or less. In other words, the configuration 1 and the like are particularly significant in a spark plug having a screw diameter of M14 or less.

  Configuration 4. The spark plug of this configuration is characterized in that, in any one of the above configurations 1 to 3, the screw diameter of the screw portion is M12 or less.

  In the spark plug in which the screw diameter of the thread portion is M12 or less as in the configuration 4, the contact area of the taper surface with the seat surface is further reduced, and thus there is a greater concern about the decrease in airtightness. However, by adopting the above configuration 1 or the like, excellent airtightness can be realized even with a spark plug having a screw diameter of M12 or less. In other words, the above configuration 1 or the like is extremely significant in a spark plug having a screw diameter of M12 or less.

Configuration 5. The spark plug manufacturing method of the present configuration includes a cylindrical insulator extending in the axial direction,
A cylindrical metal shell provided on the outer periphery of the insulator;
The metal shell is
A threaded portion for screwing into the mounting hole of the combustion device;
A tapered surface having an outer diameter that gradually decreases toward the distal end side, and a bowl-shaped seat portion that is positioned on the rear end side of the screw portion;
When the threaded portion is screwed into the mounting hole of the combustion device, the tapered surface is in contact with the seating surface of the combustion device,
Using a receiving die having an insertion hole through which the screw portion can be inserted and an annular receiving surface connected to an opening of the insertion hole, the metal fitting is inserted into the receiving die while the screw portion is inserted into the insertion hole. Pressing to the side and pressing the tapered surface against the receiving surface,
At least a portion of the receiving surface where the tapered surface is pressed has an arithmetic mean roughness of the surface of 1 μm or more and 5 μm or less, and an annular shape or a spiral shape having a length of one or more rounds. Comprising at least one of a protrusion and a recess extending along the circumferential direction of the receiving surface,
In the pressing step, the tapered surface is pressed against the receiving surface to form an annular shape or a spiral shape having a length of one or more rounds in the circumferential direction of the metal shell. Protrusions extending along the surface are formed.

  As in the configuration 6 described below, in the process of forming the caulking portion at the rear end portion of the metal shell, it has an insertion hole through which the screw portion can be inserted, and an annular receiving surface connected to the opening of the insertion hole. Using the receiving mold, the threaded portion is inserted into the insertion hole, the metal shell is pressed toward the receiving mold, and the tapered surface is pressed against the receiving surface. Here, in order to improve the airtightness, when the tapered surface is made smooth with very few irregularities, the frictional force generated between the receiving surface and the tapered surface becomes very small. Therefore, when the metal shell is pressed, the taper surface becomes slippery with respect to the receiving surface, and as a result, the meat of the seat portion is likely to get into the insertion hole. If the metal shell bites on the receiving mold, extra labor is required when removing the metal shell from the receiving mold, which may lead to a decrease in productivity. Moreover, when the meat of the seat portion enters the insertion hole, the seat portion may have large wrinkles, and as a result, the yield may be reduced.

  In this respect, according to the configuration 5, at least a part of the receiving surface where the tapered surface is pressed has an arithmetic average roughness of the surface of 1 μm or more. Therefore, the frictional force generated between the receiving surface and the tapered surface can be made sufficiently large, and slipping of the tapered surface with respect to the receiving surface can be suppressed when the metal shell is pressed. As a result, it is possible to more reliably prevent the metal shell from being bitten by the receiving mold, and to improve productivity and yield.

  In addition, when the taper surface of the receiving surface is simply pressed and uneven, the taper surface can be prevented from slipping with respect to the receiving surface. Therefore, when the manufactured spark plug is assembled to the combustion device, the adhesion of the tapered surface to the seating surface is impaired, and the airtightness may be insufficient. However, according to the configuration 5, at least a part of the portion of the receiving surface on which the tapered surface is pressed has an annular shape or a spiral shape having a length of one or more rounds, and is along the circumferential direction of the receiving surface. And at least one of a projecting portion and a concave portion extending in the direction. Therefore, after the pressing step, the tapered surface is formed with an annular shape or a spiral shape having a length of one or more rounds and extending along the circumferential direction of the metal shell. Therefore, when the manufactured spark plug is assembled to the combustion device, the annular or spiral protrusion can be brought into contact with the seat surface with a relatively large pressure, and the gap between the seat surface and the tapered surface can be made. It can seal more reliably over the entire circumference. As a result, excellent airtightness can be ensured.

  Furthermore, even if the taper surface has some wrinkles or irregularities before pressing against the receiving surface, the wrinkles or irregularities are made extremely small by the taper surface being deformed by the pressure on the receiving surface. Meanwhile, a spiral or annular protrusion can be formed on the tapered surface. That is, before the pressing step, the taper surface may be slightly wrinkled or uneven, and it is not necessary to manage the taper surface with particular care. In addition, since the arithmetic average roughness of the surface of the receiving surface is 1 μm or more, after the pressing process, the arithmetic average roughness of the tapered surface is also 1 μm or more, and it is assumed that the taper surface in this state has some wrinkles. However, a large difference does not occur in the state of the tapered surface. Therefore, it is not necessary to carefully manage the tapered surface even after the pressing step. Therefore, according to the configuration 5, the taper surface can be easily managed before and after the pressing step, and the productivity can be further improved.

  In order to realize excellent airtightness more reliably, the arithmetic average roughness of the surface of the receiving surface where the tapered surface is pressed is preferably 5 μm or less.

Configuration 6. The spark plug manufacturing method of this configuration is the above-described configuration 5, wherein in the spark plug, the insulator and the metal shell are formed by a caulking portion that is bent inward in the radial direction provided at a rear end portion of the metal shell. And are fixed,
In the pressing step, by pressing the rear end portion of the metal shell, the rear end portion of the metal shell is bent radially inward to form the crimped portion, and the tapered surface is used as the receiving surface. The protrusion is formed by pressing.

  According to the configuration 6, the caulking portion for fixing the metal shell and the insulator and the spiral or annular protrusion can be formed simultaneously. Therefore, it is not necessary to separately provide a process for forming the crimped part and a process for forming the protrusion, and the productivity can be further improved.

  Configuration 7. The spark plug manufacturing method of this configuration is characterized in that, in the above configuration 5 or 6, the thread diameter of the thread portion is M14 or less.

  When the thread diameter of the threaded portion is set to M14 or less as in the configuration 7, the surface pressure of the tapered surface with respect to the receiving surface is increased during the pressing step, and the space between the receiving surface and the tapered surface is increased. The frictional force generated in is small. Therefore, although there is a greater concern about the biting of the metal shell with respect to the receiving mold, such a concern can be eliminated by adopting the configuration 5 or the like. In other words, the above configuration 5 or the like is particularly significant when manufacturing a spark plug in which the screw diameter of the screw portion is M14 or less.

  Further, in the manufactured spark plug, the configuration of the tapered surface satisfies the above-described configuration 1 and the like. Therefore, even if the screw diameter is M14 or less and the contact area of the tapered surface with the seating surface cannot be sufficiently ensured, excellent airtightness can be realized.

  Configuration 8. The spark plug manufacturing method of this configuration is characterized in that, in any of the above configurations 5 to 7, the screw diameter of the screw portion is M12 or less.

  When the screw diameter of the thread portion is set to M12 or less as in the configuration 8, the surface pressure of the tapered surface with respect to the receiving surface becomes very large during the pressing process, and the receiving surface and the tapered surface The frictional force generated between the two is extremely small. Therefore, although there is a greater concern about the biting of the metallic shell with respect to the receiving mold, such a concern can be eliminated by adopting the configuration 5 or the like. In other words, the above configuration 5 or the like is extremely significant when manufacturing a spark plug in which the thread diameter of the thread portion is M12 or less.

  In addition, in the manufactured spark plug, the configuration of the tapered surface satisfies the above-described configuration 1 and the like. Therefore, even when the screw diameter is set to M12 or less and the contact area of the tapered surface with respect to the seating surface is very small, excellent airtightness can be realized.

It is a partially broken front view which shows the structure of a spark plug. It is a partially broken front view which shows the ignition plug assembled | attached to the internal combustion engine. It is a partially broken enlarged front view showing an ignition plug assembled to an internal combustion engine. (A) is an expanded sectional schematic diagram which shows the structure of a taper surface, (b) is the JJ sectional view taken on the line of FIG. It is sectional drawing of the metal shell etc. which show a cyclic | annular protrusion. It is an expanded sectional view of the receiving mold etc. which shows the state which set the metal shell to the receiving mold. It is a top view which shows a receiving type structure. It is a top view which shows another example of a receiving type. It is an expanded sectional view showing one process of a press process. It is a graph which shows the result of the airtightness evaluation test in the sample which changed various arithmetic mean roughness of the surface of the perimeter side field. It is a graph which shows the relationship between the screw diameter of a thread part, and the amount of leaks.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the direction of the axis CL1 of the spark plug 1 will be described as the vertical direction in the drawing, the lower side will be described as the front end side, and the upper side will be described as the rear end side.

  The spark plug 1 includes an insulator 2 as a cylindrical insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. On the side, a leg length part 13 formed with a smaller diameter than this is provided. In addition, most of the large-diameter portion 11, the middle trunk portion 12, and the leg long portion 13 of the insulator 2 are accommodated in the metal shell 3. In addition, a tapered step portion 14 is formed at a connecting portion between the middle body portion 12 and the long leg portion 13, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  Further, the insulator 2 is formed with a shaft hole 4 penetrating along the axis CL1, and a center electrode 5 is inserted and fixed to the tip end side of the shaft hole 4. The center electrode 5 includes an inner layer 5A made of a metal having excellent thermal conductivity (for example, copper, copper alloy, pure nickel (Ni), etc.) and an outer layer 5B made of an alloy containing Ni as a main component. Further, the center electrode 5 has a rod shape (cylindrical shape) as a whole, its tip end surface is formed flat, and protrudes from the tip end of the insulator 2.

  In addition, a terminal electrode 6 is inserted and fixed on the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2.

  Further, a cylindrical resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seal layers 8 and 9, respectively.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and an ignition plug 1 is assembled to a combustion device (for example, an internal combustion engine or a fuel cell reformer) on the outer peripheral surface thereof. A threaded portion (male threaded portion) 15 for attaching is formed. Further, on the rear end side of the screw portion 15, a bowl-shaped seat portion 17 having a tapered surface 16 whose outer diameter gradually decreases toward the front end side is formed. Further, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the combustion device is provided on the rear end side of the metal shell 3. A caulking portion 20 that bends inward in the radial direction is provided at the rear end portion of the metal shell 3.

  In this embodiment, in order to reduce the diameter of the spark plug 1, the metal shell 3 is reduced in diameter, and the screw diameter of the screw portion 15 is set to M14 or less, or M12 or less. Further, in order to improve the durability, the surface of the metal shell 3 is provided with a plating layer made of a metal having nickel or zinc as a main component, and 95 mass of the chromium component provided on the plating layer and contained. A trivalent chromate layer in which at least% is trivalent chromium is formed. Furthermore, in order to further improve the durability, a rust preventive oil is applied to the trivalent chromate layer.

  A tapered step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the step 14 of the metal shell 3 is locked to the step 21 of the metal shell 3. It is fixed to the metal shell 3 by caulking the rear end side opening portion radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  In addition, a substantially middle portion of the metal shell 3 is bent back at the front end portion 26, and a ground electrode 27 having a front end side surface facing the front end surface of the center electrode 5 is joined. The ground electrode 27 has a two-layer structure of an outer layer 27A made of a Ni alloy and an inner layer 27B made of a copper alloy or a pure copper which is a better heat conductive metal than the Ni alloy. Further, a spark discharge gap 28 is formed between the tip of the center electrode 5 and the tip of the ground electrode 27, and spark discharge is performed in the spark discharge gap 28 in a direction substantially along the axis CL1. It has come to be.

  Further, in the present embodiment, as shown in FIG. 2, when the screw portion 15 is screwed into a mounting hole 42 having an internal thread formed in an internal combustion engine 41 as a combustion device, the tapered surface 16 Is in close contact with the seat surface 43 of the internal combustion engine 41 so that the airtightness in the combustion chamber is maintained. In the cross section including the axis line CL1, the acute angle (inclination angle) of the angles formed between the outline line of the seat surface 43 and the axis line CL1 is the angle formed between the outline line of the tapered surface 16 and the axis line CL1. It is smaller than an acute angle (tilt angle). Therefore, when the threaded portion 15 is screwed into the mounting hole 42, the portion located on the outer peripheral side of the tapered surface 16 comes into contact with the seat surface 43. The inclination angle of the seating surface 43 is, for example, 60 °, and the inclination angle of the tapered surface 16 is, for example, 63 °.

  The seat surface 43 is formed of a relatively soft alloy (for example, about 100 Hv) mainly composed of aluminum, while the hardness of the tapered surface 16 (seat portion 17) is higher than the hardness of the seat surface 43. It is also considered a big thing. Therefore, when the screw portion 15 is screwed into the mounting hole 42, the seat surface 43 is deformed by being pressed against the tapered surface 16, and the outer peripheral side of the tapered surface 16 comes into surface contact with the seat surface 43. Specifically, when the deformation of the seating surface 43 is small, such as when the ignition plug 1 is assembled to the internal combustion engine 41 for the first time, as shown in FIG. An outer peripheral side region 16C (portion indicated by a thick line in FIG. 3) located within a range up to a portion 16B having an outer diameter of 95% of the outer diameter D1 in the outermost peripheral portion 16A is in surface contact with the seating surface 43. On the other hand, a portion on the inner peripheral side with respect to the outer peripheral side region 16 </ b> C does not necessarily contact the seat surface 43. That is, the outer peripheral region 16C is a particularly important part in terms of maintaining the airtightness in the combustion chamber. By repeatedly attaching and removing the spark plug 1 to and from the internal combustion engine 41, the seating surface 43 gradually deforms into a shape that follows the shape of the tapered surface 16, and finally, the inner surface of the tapered surface 16 becomes inner. It can be deformed to such an extent that the peripheral side contacts.

  Further, in this embodiment, FIGS. 4 (a) and 4 (b) [In FIG. 4, for convenience of illustration, the protrusion 16P is protruded from the actual position, and the number of turns is reduced from the actual position. As shown in the drawing, a spiral portion 16 having a length of one or more rounds is formed on the entire area of the tapered surface 16 including the outer peripheral side region 16C, and a protrusion 16P extending along the circumferential direction of the metal shell 3 is formed. Yes. In the present embodiment, the protrusion 16P is configured to protrude most on the tapered surface 16. Furthermore, in the cross section including the axis line CL1, the arithmetic average roughness Ra of the surface of the tapered surface 16 is 1 μm or more and 5 μm or less. Here, the arithmetic average roughness Ra of the surface of the tapered surface 16 can be measured based on the provisions of JIS B0601. Specifically, a stylus having a tip radius of 2 μm and a tip taper angle of 60 ° is brought into contact with the measurement target surface (tapered surface 16), and the diameter from the axis CL1 side along the direction orthogonal to the axis CL1. By moving toward the outside in the direction at a predetermined measurement speed, a contour curve indicating the height of each part of the tapered surface 16 with respect to a straight line orthogonal to the axis CL1 is obtained. And in the measurement object range, the arithmetic mean roughness Ra of the surface of the taper surface 16 can be obtained by obtaining the integral value of the difference of the contour curve with respect to the average line of the contour curve.

  The entire area of the tapered surface 16 refers to the entire area of the tapered surface 16 that can contact the seating surface 43. In the present embodiment, the threaded portion of the tapered surface 16 extends from the outermost peripheral portion 16A thereof. A range up to a part having an outer diameter equal to 15 screw diameters.

  Further, instead of the spiral protrusion 16P, a plurality of annular protrusions 66P extending along the circumferential direction of the metal shell 3 may be provided on the tapered surface 66 as shown in FIG. In FIG. 5, the annular protrusion 66P is provided over the entire tapered surface 66, but the outer diameter D2 is 95% of the outer diameter D2 at least from the outermost peripheral portion 66A of the tapered surface 66 to the outermost peripheral portion. What is necessary is just to be provided in the range to the area | region 66B used as a diameter (site | part which attached the dotted pattern in FIG. 5). In addition, both the spiral protrusion and the annular protrusion may be provided on the tapered surface.

  Next, the manufacturing method of the spark plug 1 comprised as mentioned above is demonstrated.

  First, the insulator 2 is molded. For example, a green body granulation material is prepared using a raw material powder mainly composed of alumina and containing a binder and the like, and a rubber compact is used to obtain a cylindrical molded body. Then, the insulator 2 is obtained by subjecting the obtained molded body to grinding, shaping the outer shape thereof, and firing the shaped molded body.

  In addition, the center electrode 5 is manufactured separately from the insulator 2. That is, the center electrode 5 is produced by forging a Ni alloy in which a copper alloy or the like for improving heat dissipation is arranged at the center.

  Then, the insulator 2 and the center electrode 5, the resistor 7, and the terminal electrode 6 obtained as described above are sealed and fixed by the glass seal layers 8 and 9. The glass seal layers 8 and 9 are generally prepared by mixing borosilicate glass and metal powder, and the prepared material is injected into the shaft hole 4 of the insulator 2 with the resistor 7 interposed therebetween. After being done, it is baked and hardened by heating in the firing furnace while pressing with the terminal electrode 6 from the rear. At this time, the glaze layer may be fired simultaneously on the surface of the rear end body portion 10 of the insulator 2 or the glaze layer may be formed in advance.

  Next, the metallic shell 3 is processed. That is, a through-hole is formed by subjecting a cylindrical metal material (for example, an iron-based material such as S17C or S25C or a stainless material) to a cold forging process, and an approximate shape is formed. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, a straight bar-shaped ground electrode 27 made of Ni alloy or the like is resistance-welded to the front end surface of the metal shell intermediate. When the welding is performed, so-called “sag” is generated. After the “sag” is removed, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 3 to which the ground electrode 27 is joined is obtained. Furthermore, a plating layer and a trivalent chromate layer are provided by plating the metal shell 3 to which the ground electrode 27 is welded. Further, rust preventive oil is applied to the surface of the metal shell 3.

  In the obtained metal shell 3, the tapered surface 16 of the seat portion 17 is not formed with the spiral protrusion 16 </ b> P, and is flat. Note that slight irregularities and wrinkles may be formed on the tapered surface 16.

  Thereafter, in the pressing step, the insulator 2 provided with the center electrode 5 and the terminal electrode 6 and the metal shell 3 provided with the ground electrode 27 are fixed.

  In the pressing step, as shown in FIG. 6, first, with the insulator 2 inserted into the metal shell 3, the distal end side of the metal shell 3 is inserted into the cylindrical receiving die 51, thereby The metal shell 3 is held.

  The receiving mold 51 includes an insertion hole 52 through which the threaded portion 15 can be inserted, and an annular receiving surface 53 that is connected to the opening of the insertion hole 52 and contacts the tapered surface 16. The receiving surface 53 is set so that the inclination angle thereof is the same as the inclination angle of the tapered surface 16 (for example, 63 °). The receiving mold 51 is made of hard steel such as hardened steel, and at least the receiving surface 53 has a hardness greater than the hardness of the tapered surface 16 of the metal shell 3.

  Furthermore, in the pressing step, the tapered surface 16 is pressed against the receiving surface 53. At least a part of the receiving surface 53 where the tapered surface 16 is pressed (in this embodiment, the entire region where the tapered surface 16 is pressed) has an arithmetic average roughness Ra of 1 μm or more to 5 μm. As shown in FIG. 7, a spiral shape having a length of one or more rounds and a projecting portion 54 and a concave portion 55 extending along the circumferential direction of the receiving surface 53 are provided. The concave portion 55 refers to a spiral groove portion formed between the protruding portions 54.

  The arithmetic average roughness Ra of the surface of the receiving surface 53 can be measured based on the provisions of JIS B0601. Specifically, the stylus having a tip radius of 2 μm and a tip taper angle of 60 ° is brought into contact with the measurement target surface (receiving surface 53), and along the direction perpendicular to the central axis of the insertion hole 52. By moving toward the radially outer side from the central axis side, a contour curve indicating the height of each part of the receiving surface 53 with respect to a straight line orthogonal to the central axis is obtained. And in the measurement object range, the arithmetic mean roughness Ra of the surface of the receiving surface 53 can be obtained by obtaining the integral value of the difference of the contour curve with respect to the average line of the contour curve.

  Further, instead of the spiral projecting portion 54 and the recessed portion 55, as shown in FIG. 8, annular projecting portions 74 that extend on the receiving surface 73 of the receiving mold 71 along the circumferential direction of the receiving surface 73, respectively. And the recessed part 75 (In addition, the recessed part 75 is good also as providing the groove-shaped part provided between the protruding parts 74). In FIG. 8, the protrusion 74 and the recess 75 are formed over the entire area of the receiving surface 73 where the tapered surface 16 is pressed, but at least the tapered surface 16 of the receiving surface 73. What is necessary is just to be provided in the site | part by which the outer peripheral side area | region 16C is pressed.

  Returning to the description of the manufacturing method, as shown in FIG. 6, with the metal shell 3 held by the receiving mold 51, the inner peripheral surface at the tip of the opening has a curved surface portion 57 corresponding to the shape of the caulking portion 20. A cylindrical pressing die 56 is mounted from above the metal shell 3. In addition, in a state where the metal shell 3 is sandwiched between the receiving die 51 and the pressing die 56, the metal shell 3 is pressed to the receiving die 51 side by the pressing die 56 with a predetermined load (for example, 30 kN or more and 50 kN or less). To do. As a result, as shown in FIG. 9, the tapered surface 16 is pressed and deformed by the receiving surface 53, and a spiral protrusion 16 </ b> P is formed on the surface of the tapered surface 16. Even if some irregularities or wrinkles are formed on the surface of the tapered surface 16, the tapered surface 16 is deformed following the receiving surface 53 in accordance with the pressing to the receiving surface 53, and the surface wrinkles or The unevenness becomes extremely small, and the arithmetic average roughness Ra of the surface of the tapered surface 16 is set to 1 μm or more and 5 μm or less. In addition, the caulking portion 20 is formed by bending the rear end side opening of the metal shell 3 inward in the radial direction, and the insulator 2 and the metal shell 3 are fixed. That is, in the present embodiment, the protrusion 16P and the caulking portion 20 are formed at the same time.

  Note that, by applying a load from the pressing die 56, the relatively thin cylindrical portion located between the seat portion 17 and the tool engaging portion 19 is curved and deformed outward in the radial direction. As a result, an axial force along the axis CL1 is applied from the metal shell 3 to the insulator 2, and as a result, the insulator 2 and the metal shell 3 are more reliably fixed.

  After fixing the metal shell 3 and the insulator 2, the ground electrode 27 is bent toward the center electrode 5, and the spark discharge gap 28 formed between the tip of the center electrode 5 and the tip of the ground electrode 27 is formed. By adjusting the size, the above-described spark plug 1 is obtained.

  As described above in detail, according to the present embodiment, in the cross section including the axis line CL1, the arithmetic average roughness Ra of the surface of the tapered surface 16 including the outer peripheral side region 16C is set to 1 μm or more. Existence is allowed. Therefore, even if a minute wrinkle is attached, there is no great difference in the state of the tapered surface 16, and it is not necessary to manage the tapered surface 16 with particular care during the manufacturing process or transportation. As a result, excellent productivity and ease of handling can be realized.

  In addition, in the present embodiment, the taper surface 16 is formed with a protrusion 16P (66P) that has an annular shape or a spiral shape of one or more rounds and extends along the circumferential direction of the metal shell 3. Accordingly, when the spark plug 1 is assembled to the internal combustion engine 41, the spiral or annular protrusion 16P (66P) of the tapered surface 16 is brought into contact with the seat surface 43 with a relatively large pressure. be able to. Furthermore, since the protrusion 16P (66P) that contacts with a relatively large pressure has an annular shape or a spiral shape of one or more rounds, the projection between the seating surface 43 and the tapered surface 16 can be more reliably performed over the entire circumference. Can be sealed. As a result, excellent airtightness can be ensured.

  Furthermore, in this embodiment, the arithmetic average roughness of the surface of the taper surface 16 is 5 μm or less. Therefore, the adhesiveness of the taper surface 16 with respect to the seat surface 43 can be sufficiently ensured, and excellent airtightness can be more reliably realized.

  In the present embodiment, a spiral or annular protrusion 16P (66P) is formed over the entire tapered surface 16. Therefore, even if the seating surface 43 is deformed by repeatedly assembling / removing the spark plug 1 to / from the internal combustion engine 41, a spiral or annular protrusion formed at any position. 16P (66P) can be brought into contact with the seating surface 43. Therefore, even when the spark plug 1 is assembled a plurality of times and the seat surface 43 is deformed, good airtightness can be maintained.

  Furthermore, when manufacturing the spark plug 1, at least a part of the receiving surface 53 of the receiving mold 51 where the tapered surface 16 is pressed has an arithmetic average roughness of the surface of 1 μm or more. Therefore, the frictional force generated between the receiving surface 53 and the tapered surface 16 can be made sufficiently large, and the sliding of the tapered surface 16 with respect to the receiving surface 53 can be suppressed when the metal shell 3 is pressed. . As a result, it is possible to more reliably prevent the metal shell 3 from being bitten by the receiving mold 51 and to improve productivity and yield. In particular, in this embodiment, since the pressing step is performed after the antirust oil is applied to the surface of the metal shell 3, the taper surface 16 becomes more slippery with respect to the receiving surface 53 in the pressing step. Even in the state, the sliding of the tapered surface 16 with respect to the receiving surface 53 can be sufficiently suppressed.

  In addition, at least a part of the portion of the receiving surface 53 where the tapered surface 16 is pressed has an annular shape or a spiral shape having a length of one or more rounds, and a protruding shape extending along the circumferential direction of the receiving surface 51. A portion 54 and a concave portion 55 (protruding portion 74 and concave portion 75) are provided. Therefore, after the pressing step, the tapered surface 16 is formed with a protrusion 16P (66P) that is annular or spiral having a length of one or more rounds and extends along the circumferential direction of the metal shell 3. It becomes. Therefore, when the manufactured spark plug 1 is assembled to the internal combustion engine 41, the annular or spiral protrusion 16P (66P) can be brought into contact with the seat surface 43 with a relatively large pressure. 43 and the taper surface 16 can be more reliably sealed over the entire circumference. As a result, excellent airtightness can be ensured.

  Furthermore, even if the taper surface 16 has some wrinkles unevenness before pressing against the receiving surface 53, the taper surface 16 is deformed by pressing against the receiving surface 53, so that the wrinkles and unevenness are reduced. The spiral or annular protrusion 16P can be formed on the tapered surface 16 while being extremely small. That is, before the pressing step, the taper surface 16 may be slightly wrinkled or uneven, and it is not necessary to manage the taper surface 16 with particular care. Further, after the pressing step, the arithmetic average roughness of the surface of the taper surface 16 is set to 1 μm or more, so that even if the taper surface 16 has a minute wrinkle, there is no great difference in the state of the taper surface 16. . Therefore, it is not necessary to carefully manage the tapered surface 16 even after the pressing step. That is, according to the present embodiment, before and after the pressing step, the taper surface 16 can be easily managed, and productivity can be further improved.

  In addition, in this embodiment, the caulking portion 20 for fixing the metal shell 3 and the insulator 2 and the spiral or annular protrusion 16P (66P) can be formed simultaneously. Therefore, it is not necessary to separately provide a process for forming the caulking portion 20 and a process for forming the spiral or annular protrusion 16P (66P), and the productivity can be further improved. .

  In addition, since at least part of the portion of the receiving surface 53 of the receiving mold 51 where the tapered surface 16 is pressed has an arithmetic average roughness of the surface of 5 μm or less, in the manufactured spark plug 1, Adhesiveness of the taper surface 16 to the surface 43 can be sufficiently ensured. Thereby, excellent airtightness can be realized more reliably.

  Next, in order to confirm the effect achieved by the above embodiment, a spiral protrusion having a length of one or more rounds is provided in the outer peripheral side region of the tapered surface, and the arithmetic average roughness of the outer peripheral side region is provided. Samples of spark plugs with various changes in Ra were prepared, and an airtightness evaluation test was performed on each sample. The airtightness evaluation test is based on the airtightness test of ISO11565, and the outline thereof is as follows. That is, the sample was assembled to the above-described aluminum test bench imitating the internal combustion engine with a tightening torque of 20 N · m, and the seating surface of the test stand was heated to 200 ° C. In this state, the pressure of 1 MPa to 4 MPa is continuously applied to the tip of the sample by air, and the amount of air leaked per minute (ml / min) between the sample (tapered surface) and the test table (seat surface) It was measured. FIG. 10 is a graph showing the relationship between the air pressure and the leakage amount in each sample. In addition, in FIG. 10, the test result of the sample which made arithmetic mean roughness Ra of the outer peripheral side area | region 0.2 micrometers is shown by a white circle, and the test result of the sample which made said arithmetic mean roughness Ra 0.5 micrometer Is indicated by a black circle, the test result of the sample having the arithmetic average roughness Ra of 1 μm is indicated by a white triangle mark, and the test result of the sample having the arithmetic average roughness Ra of 2 μm is indicated by a black triangle mark. In addition, the test result of the sample with the arithmetic average roughness Ra of 3 μm is indicated by a white square mark, the test result of the sample with the arithmetic average roughness Ra of 4 μm is indicated by a black square mark, and the arithmetic average roughness The test result of the sample with Ra of 5 μm is indicated by white diamonds, and the test result of the sample with arithmetic mean roughness Ra of 6 μm is indicated by black diamonds.

  Furthermore, Table 1 shows the evaluation of the airtightness of each sample when the air pressure is 2 MPa or 3 MPa. In Table 1, when the pressure is set to 2 MPa, a sample having a leakage amount of more than 0.5 ml / min and not more than 1.0 ml / min is evaluated as “◯” because it has good airtightness. A sample having a leakage amount of 0.5 ml / min or less was evaluated as “◎” as having excellent airtightness. In addition, when the pressure was 3 MPa, the sample having a leakage amount of 1.0 ml / min or less was evaluated as “」 ”as having excellent airtightness, and the leakage amount was 0.5 ml / min or less. These samples were evaluated as “☆” having extremely excellent airtightness. In the airtight test based on ISO11565, when the pressure is set to 2.0 MPa and the leakage amount is 2.0 ml / min or less, there is no problem in terms of airtightness. Therefore, in this test, each sample is evaluated according to a stricter standard than the standard in ISO.

  In each sample, the thread diameter of the threaded portion was M14, and the opposite side dimension of the tool engaging portion was 16 mm. Furthermore, a plating layer made of a metal mainly composed of Ni and a trivalent chromate layer were provided on the surface of the metal shell, and rust preventive oil was applied to the surface of the trivalent chromate layer. Further, the arithmetic average roughness Ra is measured by using a JIS type contact type roughness measuring instrument, and the stylus contacting the measurement target part is measured with a tip radius of 2 μm and a tip taper angle of 60 °. The speed was 0.03 mm / s. In addition, the arithmetic average roughness of the outer peripheral side region in each sample was changed by changing the arithmetic average roughness on the receiving surface of the receiving mold. In addition, the inclination angle of the seating surface on the test bench was set to 60 °, and the inclination angle of the taper surface of the sample was set to 63 ° (Note that the structure of the metal shell and the method for measuring the arithmetic average roughness are also used in the following tests. The same).

  As shown in Table 1 and FIG. 10, it was confirmed that the sample in which the arithmetic average roughness Ra of the outer peripheral region was 5 μm or less has excellent airtightness. This is because when the sample was assembled on the test bench, the spiral protrusion contacted the seating surface with a relatively large pressure, and the space between the seating surface and the tapered surface was sealed over the entire circumference. It is thought that.

  In particular, it was found that a sample having an arithmetic average roughness Ra of 4 μm or less has extremely excellent airtightness.

  Next, a sample of a spark plug (with protrusions) in which a spiral protrusion is provided in the outer peripheral region of the tapered surface and the arithmetic average roughness Ra of the outer peripheral region is variously changed, and an outer peripheral region of the tapered surface is provided. Without providing a spiral protrusion, by roughing the outer peripheral side region, to produce a spark plug sample (no protrusion) with various changes in the arithmetic average roughness Ra of the outer peripheral region, The airtightness evaluation test described above was performed after setting the air pressure to 2 MPa. Table 2 shows the amount of air leakage in each sample. In Table 2, the term “severe leakage” means that the amount of air leakage was more than 4 ml / min.

  As shown in Table 2, when the arithmetic average roughness Ra was less than 1 μm, the leakage amount was sufficiently small regardless of the presence or absence of the spiral protrusion, and good airtightness could be secured. However, when the arithmetic average roughness Ra is set to 1 μm or more, the airtightness deteriorates rapidly in the sample in which the spiral protrusion is not provided, whereas the sample in which the spiral protrusion is provided is good. It was confirmed that the airtightness can be maintained. This is considered to be due to the fact that the space between the tapered surface and the seating surface is sealed over the entire circumference by providing the spiral protrusion.

  From the result of the above test, the outer peripheral side region is defined as having an arithmetic average roughness Ra of 1 μm or more in the outer peripheral side region of the tapered surface and ensuring good airtightness while making the outer peripheral side region relatively rough. It can be said that the arithmetic average roughness Ra in is preferably 5 μm or less, and a spiral protrusion having a length of one or more rounds is provided in the outer peripheral side region.

  Moreover, it can be said that it is more preferable that arithmetic mean roughness Ra in an outer peripheral side area | region shall be 4 micrometers or less from a viewpoint of aiming at the further improvement of airtightness.

  In addition, even when an annular protrusion that extends along the circumferential direction of the metal shell is provided on the tapered surface, the space between the tapered surface and the seating surface can be sealed over the entire circumference. Therefore, it can be said that good airtightness can be realized even when the annular protrusion is provided, as in the case where the spiral protrusion is provided.

  Next, a spark plug sample (sample A) in which a spiral protrusion is provided only in the outer peripheral region of the tapered surface, and a spark plug sample (sample B) in which a spiral protrusion is provided over the entire taper surface. ). And after changing the number of times of assembling of the sample to the test table to 1, 100, 200, 300, or 400 times, the above airtightness evaluation test was performed with the air pressure set to 2 MPa. . Table 3 shows the test results of the test. Note that the number of times of assembling is one when the sample is assembled for the first time on the test bench. The number of times of assembling is that the sample is repeatedly assembled and removed from the test table, and the sample is assembled to the test table several times (for example, 100 times or 200 times). The state that is attached.

  As shown in Table 3, sample B provided with a spiral protrusion over the entire taper surface can maintain good airtightness even when it is assembled multiple times to the test bench. I understood. This is because the spiral protrusion is formed over a wide range, and even if the test table is deformed due to repeated assembly, the spiral protrusion is the test table (seat surface). This is considered to be due to the fact that the entire circumference was closely adhered to. Even when the protrusion is annular, it is considered that the same effect can be obtained.

  From the results of the above test, it can be said that it is preferable to provide a spiral or annular protrusion over the entire taper surface so that good airtightness can be maintained even when the assembly is performed a plurality of times.

  Next, a sample of a spark plug (sample C) in which a spiral protrusion is provided over the entire tapered surface and the arithmetic average roughness Ra of the surface of the tapered surface is 4 μm, and an annular shape is formed over the entire tapered surface. And a sample (sample D) having an arithmetic mean roughness Ra of 4 μm on the surface of the tapered surface, and roughening the entire tapered surface without providing a spiral or annular protrusion. Thus, a spark plug sample (sample E) having an arithmetic mean roughness Ra of 4 μm on the surface of the tapered surface was prepared with a thread diameter of the threaded portion of M18, M14, or M12. Each sample was subjected to the above airtightness evaluation test at an air pressure of 2 MPa. Table 4 and FIG. 11 show the test results of the test. In FIG. 11, the graph showing the test result of sample C is hatched, a dotted pattern is added to the graph showing the test result of sample D, and a lattice pattern is attached to the graph showing the test result of sample E. did.

  As shown in Table 4 and FIG. 11, in the sample E in which the spiral or annular protrusion is not provided, as the screw diameter of the screw portion becomes smaller (that is, as the contact area of the tapered surface with respect to the seat surface becomes smaller). However, the samples C and D provided with a spiral or annular protrusion had a screw diameter of M14 or M12, and the contact area was small on the taper surface with respect to the seat surface. However, it was revealed that excellent airtightness can be secured.

  From the results of the above test, it is effective to provide an annular or spiral protrusion on the tapered surface of the spark plug in which the screw diameter of the screw portion is M14 or less and airtightness is likely to be reduced. It can be said that it is very effective to provide an annular or spiral protrusion on the tapered surface in a spark plug having a diameter of M12 or less and extremely easy to cause a decrease in airtightness.

  Next, the screw diameter of the thread portion is provided by using a receiving die in which a spiral projecting portion and a concave portion are provided in a portion of the receiving surface where the tapered surface is pressed and the arithmetic average roughness Ra of the portion is variously changed. By forming the crimped portion on the metal shell made of M18, M14, or M12, the step of fixing the metal shell and the insulator (pressing step) is performed a plurality of times, and the seat portion with respect to the insertion hole of the receiving mold is The ratio (incidence rate of occurrence of eating) that occurred (inclusion of eating) was measured. Table 5 shows the results of the test. The load when the metal shell is received and pressed to the mold side by the pressing die is 55 kN when the screw diameter is M18, 40 kN when the screw diameter is M14, and the screw diameter is M12. 35 kN.

  As shown in Table 5, when the arithmetic average roughness Ra of the portion of the receiving surface where the tapered surface is pressed is 1 μm or more, the biting rate is 0%, and the metal shell biting against the receiving die It was found that can be suppressed extremely effectively. This is considered to be because the frictional force between the receiving surface and the taper surface is sufficiently large, and the slip of the taper surface with respect to the insertion hole side is suppressed.

  Further, from the test result when the arithmetic average roughness Ra is 0.2 μm or 0.5 μm, when the screw diameter of the screw portion is M14, the occurrence rate of the bite becomes large, and the screw portion When the screw diameter was M12, it was confirmed that the occurrence rate of biting was extremely large. However, when the arithmetic average roughness Ra of the portion of the receiving surface where the tapered surface is pressed is set to 1 μm or more, the metal shell can be obtained even under such a condition that the metal shell is very likely to bite against the receiving die. Was effectively suppressed.

  In the metal shell that has undergone the pressing step, the arithmetic average roughness Ra of the portion of the tapered surface that contacts the receiving surface is equal to the arithmetic average roughness Ra of the portion of the receiving surface that is pressed against the tapered surface. It becomes. For example, when the arithmetic average roughness Ra of the portion of the receiving surface where the tapered surface is pressed is 5 μm, the arithmetic average roughness Ra of the portion of the tapered surface that contacts the receiving surface is also 5 μm. Here, as described above, in terms of ensuring good airtightness, it is preferable to set the arithmetic average roughness Ra of the surface of the tapered surface to 5 μm or less (see Table 1 and FIG. 10). Therefore, in the spark plug manufactured through the pressing step, the taper surface of the receiving surface is pressed in the receiving surface from the viewpoint of improving the adhesion of the tapered surface to the seat surface and ensuring excellent airtightness. It can be said that the arithmetic average roughness Ra is preferably 5 μm or less.

  From the result of the above test, from the viewpoint of ensuring excellent airtightness in the manufactured spark plug while more reliably preventing biting of the metal shell against the receiving mold and realizing excellent productivity. At least a part of the portion where the tapered surface is pressed has an arithmetic average roughness of the surface of 1 μm or more and 5 μm or less, and has a ring shape or a spiral shape, and is a protruding portion extending along the circumferential direction of the receiving surface It can be said that it is preferable to have at least one of the recess and the recess.

  The above-described configuration is particularly effective when the screw diameter of the screw portion is M14 or less and the metal shell is more easily bited by the receiving die, and the screw diameter of the screw portion is M12 or less. It can be said that it is very effective in a condition where the metal shell is extremely susceptible to biting.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the spiral protrusion 16P is formed over the entire tapered surface 16, but the spiral protrusion 16P only needs to be formed at least in the outer peripheral region 16C. .

  (B) In the above embodiment, the protruding portion 54 and the recessed portion 55 are formed over the entire area of the receiving surface 53 where the tapered surface 16 is pressed. It is good also as forming the protruding part 54 and the recessed part 55 only in the site | part to which is pressed.

  (C) In the above-described embodiment, the receiving surface 53 is provided with the protruding portion 54 and the recessed portion 55, but only one of the protruding portion and the recessed portion may be provided. In this case, in the pressing step, the tapered surface 16 enters a groove-like portion provided between the recesses and the protrusions, so that a spiral or annular protrusion is formed.

  (D) In the above embodiment, in the pressing step, the insulator 2 and the metal shell 3 are formed by forming the crimped portion 20 without performing heating of the metal shell 3 (so-called cold crimping). Is fixed. On the other hand, in the pressing step, the insulator 2 and the metal shell 3 are fixed by forming the crimped portion 20 while applying current heating to the metal shell 3 (so-called hot crimping). It is good as well. In the case of performing cold crimping, it is necessary to apply a larger load from the pressing die 56 to the metal shell 3 than in the case of performing hot crimping. Biting of the metal fitting 3 is more likely to occur. Therefore, it is particularly significant to adopt the technical idea of the present invention when the insulator 2 and the metal shell 3 are fixed by performing cold crimping in the pressing step.

  (E) In the said embodiment, although the screw diameter of the screw part 15 is M14 or less or M12 or less, the screw diameter of the screw part 15 is not limited to this.

  (F) In the above embodiment, the plating layer and the trivalent chromate layer are formed on the surface of the metal shell 3, but the plating layer and the trivalent chromate layer may not be provided. Moreover, it is good also as not applying rust prevention oil.

  (G) In the above embodiment, the case where the ground electrode 27 is joined to the distal end portion of the metal shell 3 is embodied. However, a part of the metal shell (or the tip metal fitting previously welded to the metal shell is used. The present invention is also applicable to the case where the ground electrode is formed by cutting out a part of the ground (for example, Japanese Patent Application Laid-Open No. 2006-236906).

  (H) In the above embodiment, the tool engagement portion 19 has a hexagonal cross section, but the shape of the tool engagement portion 19 is not limited to such a shape. For example, it may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)].

1 ... Spark plug 2 ... Insulator (insulator)
DESCRIPTION OF SYMBOLS 3 ... Main metal fitting 15 ... Screw part 16 ... Tapered surface 16P ... Projection part 17 ... Seat part 41 ... Internal combustion engine (combustion apparatus)
42 ... Mounting hole 43 ... Seat surface 51 ... Receiving mold 52 ... Insertion hole 53 ... Receiving surface 54 ... Projection 55 ... Recess CL1 ... Axis

Claims (8)

A cylindrical insulator extending in the axial direction;
A cylindrical metal shell provided on the outer periphery of the insulator;
The metal shell is
A threaded portion for screwing into the mounting hole of the combustion device;
A tapered surface having an outer diameter that gradually decreases toward the distal end side, and a bowl-shaped seat portion that is positioned on the rear end side of the screw portion;
When the threaded portion is screwed into the mounting hole of the combustion device, the tapered surface is a spark plug that contacts the seat surface of the combustion device,
In the range from at least the outermost peripheral portion of the tapered surface to a portion having an outer diameter of 95% of the outer diameter at the outermost peripheral portion, the taper surface has a ring shape or a spiral shape having a length of one or more rounds, and the main body A protrusion extending along the circumferential direction of the metal fitting is formed,
The spark plug characterized in that, in a cross section including the axis, the arithmetic average roughness of the surface of the tapered surface within the range is 1 μm or more and 5 μm or less. The protrusion is formed over the entire tapered surface,
2. The spark plug according to claim 1 , wherein an arithmetic average roughness of a surface of the tapered surface is 1 μm or more and 5 μm or less.
  The spark plug according to claim 1 or 2, wherein a screw diameter of the thread portion is M14 or less.   The spark plug according to any one of claims 1 to 3, wherein a screw diameter of the thread portion is M12 or less. A cylindrical insulator extending in the axial direction;
A cylindrical metal shell provided on the outer periphery of the insulator;
The metal shell is
A threaded portion for screwing into the mounting hole of the combustion device;
A tapered surface having an outer diameter that gradually decreases toward the distal end side, and a bowl-shaped seat portion that is positioned on the rear end side of the screw portion;
When the threaded portion is screwed into the mounting hole of the combustion device, the tapered surface is in contact with the seating surface of the combustion device,
Using a receiving die having an insertion hole through which the screw portion can be inserted and an annular receiving surface connected to an opening of the insertion hole, the metal fitting is inserted into the receiving die while the screw portion is inserted into the insertion hole. Pressing to the side and pressing the tapered surface against the receiving surface,
At least a portion of the receiving surface where the tapered surface is pressed has an arithmetic mean roughness of the surface of 1 μm or more and 5 μm or less, and an annular shape or a spiral shape having a length of one or more rounds. Comprising at least one of a protrusion and a recess extending along the circumferential direction of the receiving surface,
In the pressing step, the tapered surface is pressed against the receiving surface to form an annular shape or a spiral shape having a length of one or more rounds in the circumferential direction of the metal shell. A method for manufacturing a spark plug, characterized by forming a protrusion extending along the projection. In the spark plug, the insulator and the metal shell are fixed by a caulking portion that is bent inward in the radial direction provided at a rear end portion of the metal shell,
In the pressing step, by pressing the rear end portion of the metal shell, the rear end portion of the metal shell is bent radially inward to form the crimped portion, and the tapered surface is used as the receiving surface. The method for manufacturing a spark plug according to claim 5, wherein the protrusion is formed by pressing.   The method for manufacturing a spark plug according to claim 5 or 6, wherein a screw diameter of the thread portion is M14 or less.   The spark plug manufacturing method according to any one of claims 5 to 7, wherein a screw diameter of the screw portion is M12 or less.

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